Re: [PATCH] Add SGX selftest `augment_via_eaccept_long`

[Jarkko Sakkinen <jarkko@kernel.org>]

On Thu, Aug 11, 2022 at 04:36:57AM +0300, Jarkko Sakkinen wrote:
> On Thu, Aug 11, 2022 at 04:01:15AM +0300, Jarkko Sakkinen wrote:
> > On Wed, Aug 10, 2022 at 12:09:56AM +0000, Dhanraj, Vijay wrote:
> > > 
> > > 
> > > > -----Original Message-----
> > > > From: Jarkko Sakkinen <jarkko@kernel.org>
> > > > Sent: Tuesday, August 9, 2022 11:53 AM
> > > > To: Dhanraj, Vijay <vijay.dhanraj@intel.com>
> > > > Cc: linux-sgx@vger.kernel.org; Chatre, Reinette
> > > > <reinette.chatre@intel.com>; dave.hansen@linux.intel.com; Huang, Haitao
> > > > <haitao.huang@intel.com>
> > > > Subject: Re: [PATCH] Add SGX selftest `augment_via_eaccept_long`
> > > > 
> > > > On Tue, Aug 09, 2022 at 05:08:21PM +0000, Dhanraj, Vijay wrote:
> > > > >
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Jarkko Sakkinen <jarkko@kernel.org>
> > > > > > Sent: Tuesday, August 9, 2022 9:10 AM
> > > > > > To: Dhanraj, Vijay <vijay.dhanraj@intel.com>
> > > > > > Cc: linux-sgx@vger.kernel.org; Chatre, Reinette
> > > > > > <reinette.chatre@intel.com>; dave.hansen@linux.intel.com; Huang,
> > > > > > Haitao <haitao.huang@intel.com>
> > > > > > Subject: Re: [PATCH] Add SGX selftest `augment_via_eaccept_long`
> > > > > >
> > > > > > On Tue, Aug 09, 2022 at 01:45:35PM +0300, Jarkko Sakkinen wrote:
> > > > > > > On Mon, Aug 08, 2022 at 06:29:13PM +0300, Jarkko Sakkinen wrote:
> > > > > > > > On Mon, Aug 08, 2022 at 01:00:54PM +0000, Dhanraj, Vijay wrote:
> > > > > > > > >
> > > > > > > > > > -----Original Message-----
> > > > > > > > > > From: Jarkko Sakkinen <jarkko@kernel.org>
> > > > > > > > > > Sent: Monday, August 8, 2022 5:18 AM
> > > > > > > > > > To: Dhanraj, Vijay <vijay.dhanraj@intel.com>
> > > > > > > > > > Cc: linux-sgx@vger.kernel.org; Chatre, Reinette
> > > > > > > > > > <reinette.chatre@intel.com>; dave.hansen@linux.intel.com;
> > > > > > > > > > Huang, Haitao <haitao.huang@intel.com>
> > > > > > > > > > Subject: Re: [PATCH] Add SGX selftest
> > > > > > > > > > `augment_via_eaccept_long`
> > > > > > > > > >
> > > > > > > > > > On Thu, Aug 04, 2022 at 01:14:56PM -0700,
> > > > > > > > > > vijay.dhanraj@intel.com
> > > > > > wrote:
> > > > > > > > > > > From: Vijay Dhanraj <vijay.dhanraj@intel.com>
> > > > > > > > > > >
> > > > > > > > > > > This commit adds a new test case which is same as
> > > > > > > > > > > `augment_via_eaccept` but adds more number of EPC pages to
> > > > > > > > > > > stress test
> > > > > > > > > > `EAUG` via `EACCEPT`.
> > > > > > > > > > >
> > > > > > > > > > > Signed-off-by: Vijay Dhanraj <vijay.dhanraj@intel.com>
> > > > > > > > > > > Signed-off-by: Haitao Huang <haitao.huang@linux.intel.com>
> > > > > > > > > >
> > > > > > > > > > Hey, to reproduce the original issue: does it reproduce on
> > > > > > > > > > VM or should I run baremetal kernel?
> > > > > > > > > >
> > > > > > > > > > BR, Jarkko
> > > > > > > > >
> > > > > > > > > Hi Jarkko, The issue should be reproducible on baremetal kernel.
> > > > > > > >
> > > > > > > > Thanks.
> > > > > > >
> > > > > > > I need comment out other tests in order to make sane out of this
> > > > > > > :-)
> > > > > > >
> > > > > > > Mentioning this because came into realization that stress tests
> > > > > > > should be IMHO moved each to a separate binary (so that they can
> > > > > > > be run separately). Just a note (TODO) to myself.
> > > > > > >
> > > > > > > I'll work on this today again and *possibly* split your test to
> > > > > > > its own application to get a starting point for forementioned.
> > > > > >
> > > > > > I got
> > > > > >
> > > > > > #  RUN           enclave.augment_via_eaccept_long ...
> > > > > > # main.c:1241:augment_via_eaccept_long:test enclave: total_size =
> > > > > > 8192,
> > > > > > seg->size = 8192 # main.c:1241:augment_via_eaccept_long:test enclave:
> > > > > > total_size = 12288, seg->size = 4096 #
> > > > > > main.c:1241:augment_via_eaccept_long:test enclave: total_size =
> > > > > > 36864,
> > > > > > seg->size = 24576 # main.c:1241:augment_via_eaccept_long:test enclave:
> > > > > > total_size = 40960, seg->size = 4096 #
> > > > > > main.c:1259:augment_via_eaccept_long:mmaping pages at end of
> > > > enclave...
> > > > > > # main.c:1273:augment_via_eaccept_long:Entering enclave to run
> > > > > > EACCEPT for each page of 8589934592 bytes may take a while ...
> > > > > > #            OK  enclave.augment_via_eaccept_long
> > > > > >
> > > > > > The CPU used for testing was according to /proc/cpuinfo:
> > > > > >
> > > > > > model name      : Intel(R) Xeon(R) Gold 6338 CPU @ 2.00GHz
> > > > > >
> > > > > > I have couple of queries:
> > > > > >
> > > > > > 1. Is it possible to get dmesg output?
> > > > > I did check the dmesg output but couldn't find anything related to the
> > > > failure. Just the general log messages.
> > > > >
> > > > > > 2. Do I have to repeat the test multiple times, or does it
> > > > > >    occur unconditionaly?
> > > > > >
> > > > > I was able to repro every time but it was a bit sporadic for Haitao.
> > > > >
> > > > > > BR, Jarkko
> > > > >
> > > > > Also, did you set the PRMRR size to 2GB per socket in the BIOS? The
> > > > > issue is only reproduced for oversubscribed scenario. When I set my
> > > > > PRMRR to 64GB per socket, I wasn't able to repro the issue.
> > > > 
> > > > I need to revisit this.
> > > > 
> > > > Can you simply run test_sgx with gdb and see where it hits?
> > > > HOST_CFLAGS has apparently "-g" already.
> > > > 
> > > > > Regards, Vijay
> > > > 
> > > > BR, Jarkko
> > > 
> > > I am able to repro the issue when I reduce the PRMRR to 2B/socket but not but not able to break on the assertion failure with gdb. I also enabled debug attribute in the secs but still no avail. Anything I am missing here?
> > > 
> > > diff --git a/tools/testing/selftests/sgx/load.c b/tools/testing/selftests/sgx/load.c
> > > index 7de1b15c90b1..c4bccd3f5f17 100644
> > > --- a/tools/testing/selftests/sgx/load.c
> > > +++ b/tools/testing/selftests/sgx/load.c
> > > @@ -87,7 +87,7 @@ static bool encl_ioc_create(struct encl *encl)
> > >  
> > >         memset(secs, 0, sizeof(*secs));
> > >         secs->ssa_frame_size = 1;
> > > -       secs->attributes = SGX_ATTR_MODE64BIT;
> > > +       secs->attributes = SGX_ATTR_MODE64BIT | SGX_ATTR_DEBUG;
> > >         secs->xfrm = 3;
> > >         secs->base = encl->encl_base;
> > >         secs->size = encl->encl_size;
> > > 
> > > Regards, Vijay
> > 
> > I get also full pass with 2GB configuration (and also observed that 
> > kselftest runs much faster with this configuration).
> > 
> > But I looked at sgx_alloc_epc_page() and saw this:
> > 
> >                if (list_empty(&sgx_active_page_list))
> >                         return ERR_PTR(-ENOMEM);
> > 
> >                 if (!reclaim) {
> >                         page = ERR_PTR(-EBUSY);
> >                         break;
> >                 }
> > 
> > In sgx_vma_fault(), when running completely out of reclaimable pages, this
> > causes VM_FAULT_SIGBUS returned instead of VM_FAULT_NOPAGE:
> > 
> > 	entry = sgx_encl_load_page(encl, addr, vma->vm_flags);
> > 	if (IS_ERR(entry)) {
> > 		mutex_unlock(&encl->lock);
> > 
> > 		if (PTR_ERR(entry) == -EBUSY)
> > 			return VM_FAULT_NOPAGE;
> > 
> > 		return VM_FAULT_SIGBUS;
> > 	}
> > 
> > Not sure if those should be re-ordered that would keep the process stuck up
> > until there is something to reclaim. Now we use NOPAGE to address situation
> > when there is actually something to reclaim but because of locking side of
> > things we pass reclaim=false to sgx_alloc_epc_page().
> > 
> > So this is kind of OOM behaviour how it works now instead of stalling
> > processes.
> 
> Right, I looked at the original email at was really a page fault
> that was catched. The above theory cannot possibly hold, as the
> process does not exit with a bus error.
> 
> I looked next to sgx_encl_eaug_page(), and found this:
> 
>         encl_page = sgx_encl_page_alloc(encl, addr - encl->base, secinfo_flags);
>         if (IS_ERR(encl_page))
>                 return VM_FAULT_OOM;
> 
> This is AFAIK the only code path in sgx_vma_fault() flow that
> allocates non-EPC memory, and the code paths where EPC allocation
> fails the result would be SIGBUS.
> 
> So perhaps allocation is failing here. You could pretty easily
> trace allocations with bpftrace and kretprobe to see if this is
> what is happening, e.g. in one terminal:
> 
> sudo bpftrace -e 'kr:sgx_encl_page_alloc /retval != 0/ { printf("%d\n", retval); }'

Should be

sudo bpftrace -e 'kr:sgx_encl_page_alloc /(long)retval < 0/ { printf("%d\n", retval); }'

BR, Jarkko